---
title: "Comparing lengths by measuring"
description: "Measure to determine how much longer one object is than another, expressing the length difference in terms of a standard length unit"
canonical: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4
source: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4.md
retrieved: 2026-10-19
---

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# Comparing lengths by measuring

Measure to determine how much longer one object is than another, expressing the length difference in terms of a standard length unit

Subject: Mathematics · Area: Measurement · Ages 7 to 8
Page: https://lightmysky.com/learn/mathematics/comparing-lengths-by-measuring-mt_xWg0lI_gG4

## Ready when they can

- Measure two objects and calculate the difference in length
- Express the difference using the correct unit (e.g. '7 cm longer')
- Solve a comparison problem: 'How much taller is the bookshelf than the desk?'

## Lesson: Comparing lengths by measuring

You already know how to measure things with a ruler. Now you will compare two lengths. Measure each object in the same unit, like centimeters. Then subtract the smaller number from the bigger number. That number tells you how much longer one thing is.

*(drawing: The flower is 15 cm tall. The leaf is 6 cm long. 15 minus 6 is 9, so the flower is 9 cm taller than the leaf.)*

**Example.** Mia measures her book and her notebook. The book is 20 cm long. The notebook is 13 cm long. She subtracts: 20 minus 13 equals 7. The book is 7 cm longer than the notebook.

**Tip.** Always measure both objects with the same unit, like centimeters for both. Then your subtraction gives a fair answer, and remember to say the unit, like '7 cm longer'.

**Recap.** Measure both objects in the same unit, then subtract to find how much longer one is.

## Practice

14 questions on this page, each with its working shown.

## Needs first

- [Measuring length (age 7+)](https://lightmysky.com/learn/mathematics/measuring-length-age-7-mt_e4x3l2JeLI)
- [Ordering and Comparing Lengths](https://lightmysky.com/learn/mathematics/ordering-and-comparing-lengths-mt_skYly2Qm01)

## Opens up

- [Length word problems within 100](https://lightmysky.com/learn/mathematics/length-word-problems-within-100-mt_DLcEzmmj2r)